The present invention relates to an optical module, a board mounted optical module, and method of assembly of an optical module. More specifically, the invention relates to an optical module for transmitting or receiving an optical signal, and a board mounted optical module of this kind, and to a method of assembly of an optical module of this kind.
Because of explosive use of the Internet and portable telephones, the construction of optical communication systems that offer high speed and large capacity have been promoted rapidly, and, hence, an even further reduction in the cost of optical components that are to be used in such systems is desired. On the other hand, in the board mounting process, since the jackets of optical fibers used in the optical modules have a low heat resistance, it is difficult to employ the convenient, low-cost reflow mounting process with the use of solder (i.e. mounting a component on a mount board by the solder reflow process) that is widely used in mounting electronic components. For this reason, although it becomes costly, a technique of individually mounting, only the optical modules has been adopted. Moreover, since it is difficult to automate a process of reeling the optical fiber on the mount board, the assembly process was complicated.
K. Kurata et al. have reported an optical module, which has a simplified connector structure that enables an optical fiber to be detachably connected and which is compliant with the mounting process using reflow soldering (hereinafter referred to as xe2x80x9ccompliant with the reflow mounting processxe2x80x9d), in IEEE Trans. CPMT, vol.19, p.524 (1966). FIG. 1 herein shows an example of board mounting with the use of an optical module, as described above, which is compliant with the reflow mounting process, and the housing configuration of the mount boards in optical transmission equipment. Optical modules 31 compliant with the reflow mounting process together with electronic components, such as an IC 20, an IC 21, etc., are mounted on a mount board 6 collectively by the solder reflow process. An electric connector 22, which has electric connection pins 23, is mounted on the mount board 6, and an adapter 29 for optical connection is fixed to the mount board 6 with screws. After that, a simplified connector 30 terminating an optical fiber 27 for a module is attached to the optical module 31, and a standard optical connector 1 that terminates the other end of the fiber is inserted in the adapter 29. Then, the mount board 6 on which each component is mounted is inserted along guides 28 mounted on the enclosure of the optical communication equipment to establish a connection between the adapter 29 for optical contact and the standard optical connector 1 of the optical fiber 27 supported on a connector fixed post 25 of the enclosure, as well as the connection between the electric connection pins 23 and an electric connector 24 of the electric wiring 26 supported on the same.
This structure has the following features.
(1) The optical module 31 and the electronic components can be reflow mounted collectively on the mount board 6.
(2) The adapter 29 for achieving optical contact is fixed on the mount board 6 with screws.
(3) The simplified connector 30 of the optical module 31 and the adapter 29 for optical contact are connected with the optical fiber 27.
More specifically, the simplified connector 30 attached to one end of this fiber 27 and the optical module 31 are optically connected, and the standard optical connector 1 provided at the other end thereof is optically connected to the optical adapter 29.
In structures like this, because the optical fiber is detachably connected and the structure is compliant with the reflow mounting process, there is the advantage that the optical modules can be reflow mounted with electronic components collectively. However, since the fiber 27 intervenes between the optical module 31 and the adapter 29, there is a problem that the reeling process for supply of the fiber 27 is troublesome. Moreover, since this configuration requires a portion where the fiber 27 is arranged, there is a problem that the mount board becomes larger by that amount, which is contrary to the object of miniaturization of the optical module.
Here, the reason for providing the fiber 27 in this way can be ascribed to the following fact. In the above-described optical module 31, which is devised to be compliant with the reflow mounting process, the mechanical fixation strength to the mount board for direct optical connection with an enclosure is structurally insufficient. Therefore, this module doesn""t accommodate a receptacle part which a normal optical connector is directly attached to and detached from. That is, in this construction, attachment/detachment of the normal optical connector 1 is performed through the intermediary of the separately provided optical adapter 29.
Moreover, in the optical module described in Japanese Patent Prepublication No. 5-335603, the optical module has a plate-like connection part that contacts a wide area of the mount board during the reflow process in order to increase the mechanical connection strength to the mount board. FIG. 2 shows its structure. A package main body 42 is provided with an optical connector 43 capable of being detachably connected to an external optical connector, and further comprises lead parts 44a for making connection with a circuit board 41 and a plate-like connection part 44b that is to be soldered to the circuit board 41 during the reflow process and that has a large contact area to reinforce the mechanical connection strength. However, it is difficult to miniaturize this optical module because the connection part 44b having a large contact area needs to be mounted on the circuit board, and it is likely that the module may move in the plane of the board during the reflow process; therefore this, module is not suitable for connection with an enclosure that uses a multiplex connector.
On the other hand, the optical module disclosed in the Japanese Patent Prepublication No. 8-57746 and the optical module disclosed in the Japanese Patent Prepublication No. 8-15578 have receptacle structures that allow the attachment/detachment of optical fibers with respect to the main bodies, wherein both electric wiring pins and stud pins for fixing the receptacle part ensure the mechanical strength that can stand a stress at the time of the attachment/detachment of the optical fiber. Although the problem of the reeling process in the supply of optical fiber is solved in the optical modules as described above, the optical module needs to be mounted separately and so it is difficult to mount the optical module together with electronic components collectively using the solder reflow process.
With the above-mentioned conventional technology, by providing an attaching/detaching mechanism for an optical fiber whose heat resistance is low and a reflow mounting mechanism, the optical fiber together with the electronic components can be reflow mounted collectively. However, as shown in FIG. 1, in such an example where a large stress is applied to the optical module when the mount board is attached to and detached from the enclosure, the reflow mounting only by soldering is considered to be insufficient in terms of the mechanical fixation strength of the optical module to the mount board. Therefore, to circumvent this problem, a configuration is adopted wherein an optical adapter for external connection is provided separately and this adapter is connected to the optical module via an optical fiber. Now, with this structure, a step for connection of an optical fiber will newly occur, and hence the troublesome reeling process in the supply of the optical fiber and the screw fastening process of the optical adapter still remains necessary. Consequently, with this structure, it is difficult to reduce the cost of mounting. Furthermore, it is very likely that the height and the horizontal location of the optical modules may vary when being mounted on a mount board. Especially, when a multiplex optical connector is used, there is a concern that the stress may increase at the time of the attachment/detachment of the optical fiber because of the variation of relative positions of the receptacle parts.
On the other hand, in the above-mentioned conventional technology for mounting the optical module whereby the optical module main body is fixed by electric terminal pins and stud pins, the mechanical strength at the time of the attachment/detachment of the optical fiber is sufficient. However, there exists a problem in that the collective reflow mounting of the optical module together with the other electronic components is difficult due to its pin structure.
It is an object of the present invention to provide an optical module etc. which is capable of being reflow mounted on a mount board (hereinafter referred to as xe2x80x9creflow-mounted on a boardxe2x80x9d) together with electronic components collectively and securing a mechanical strength that can bear a large stress at the time of the attachment/detachment of the optical fiber. With this construction, a low-cost mounting of the optical module can be realized, eliminating problems, such as troublesome screw fastening of the optical module, the reeling process of the optical fiber, etc. Furthermore, a structure is provided whereby the height and the horizontal position of the optical module can be controlled accurately when being reflow mounted, especially suppressing the stress of the optical module at the time of the attachment/detachment of the multiplex optical connector.
Firstly, terms are defined.
A stud means a pillar (a structure for supporting something).
A land means a printed wire part on the board to which a component is to be soldered when a tip component etc. is mounted on the board by soldering. This is a normally used term in the technical filled of solder mounting etc. In the reflow surface mounting, the term land indicates an island part on which solder is printed.
The means for solving the problem is as follows.ps
(1) FIG. 3 and FIG. 4 show a typical construction. In these figures, an optical module 19 is provided with a receptacle part 2 to which the optical connector 1 is detachably connected. This optical module 19 is provided with electric terminals 4 that can be surface mounted on the mount board 6. The electric terminals 4 are located in positions corresponding to lands 8 on the mount board 6. The optical module 19 is provided with stud parts 5. On the mount board 6, fixing holes 7 are provided for securing the optical module 19 on the mount board 6 through the intermediaries of the studs 5 thereof, and the holes 7 are constructed so as to fit the studs 5. In this construction, the studs 5 of the optical module 19 are made to fit in the mount board 6, and then solder between the electric terminals 4 and the lands 8 is melted, whereby the optical module 19 is reflow mounted on the mount board 6. According to such a construction, the above-mentioned problem can be eliminated, and hence the object of the present invention can be achieved.
(2) In such a structure, more specifically, it is also possible to adopt a construction wherein the studs 5 are formed together with the receptacle parts 2 and the optical module main body 3 in a single structural combination. Here, it is requisite to provide the stud parts 5 on the optical module main body 3, but it is optional to provide the stud parts 5 also on the receptacle part 2. Naturally, the optional provision is more effective.
(3) Moreover, it is also possible to form the stud part 5, the receptacle part 2, and the optical module main body 3 into a single structural combination with a resin material or a plastic material.
(4) Preferably, the number of studs 5 is three or more. The larger the number, the more desirable the studs are to fulfill the original function of the stud.
(5) As shown in FIG. 5, forming stud parts 9 into a taper shape is a feature of one embodiment of the present invention.
(6) As shown in FIG. 6, it is also possible to adopt a construction where stud parts 10 fit the fixing holes 7 of the mount board 6 and each stud 10 is provided with flanges. When a stud 10 is inserted in a hole 7, both sides of the mount board 6 contact those flanges, and thereby the stud 10 is made to fit in the mount board 6.
(7) It is also possible to adopt a construction, as shown in FIG. 7, where stud parts 11 with a flange fit the fixing holes 7 of the mount board 6. The flange is formed so as to contact one of the planes of the mount board 6.
(8) It is also possible to adopt a configuration where stud parts 13 and stud parts 14, each one of which is able to fit the other, are provided on the optical modules, as shown in FIG. 8 and FIG. 9, and when the two optical modules 19 are mounted on the front side and on the rear side of the mount board 6 through the intermediaries of the fixing holes 7, the two stud parts 13, 14 of the two optical modules 19 fit together to effect the fixation of the two optical modules an the mount board 6.
(9) For the configuration of the mutually fitting studs, it is possible to adopt a configuration where the stud parts 13 and the stud parts 14 are arranged at symmetrical locations with respect to a central axis A-Axe2x80x2 of the optical module, as shown in FIG. 10 and FIG. 11. Moreover, as shown in FIG. 12 and FIG. 13, it is also possible to adopt a configuration where the stud parts 5 are not arranged symmetrically with respect to the central axis A-Axe2x80x2of the optical module.
(10) As shown in FIG. 3, it is possible to adopt a configuration where the electric terminals 4 are led out through the sides of the optical module 19 as an electric terminal structure compliant with the surface mounting process or reflow mounting process. Moreover, as shown in FIG. 14 and 15, it is possible to adopt a configuration where lead-shaped electric terminals 15 or land-shaped electric terminals 16 protrude from the underside (or bottom face) of the optical module 19 as an electric terminal structure compliant with the surface mounting process or reflow mounting process.
(11) As shown in FIG. 16, it is also possible to adopt a structure where a multiplex receptacle part 18 consisting of a plurality of optical connection parts, that is, enabling a plurality of optical connectors to be attached thereto or detached therefrom, is provided so as to make possible the attachment/detachment of a plurality of discrete connectors or a multiplex connector 17.
(12) As shown in FIG. 17, it is also possible to adopt a configuration where a plurality of optical modules 19 according to the present invention are mounted on the mount board 6.
(13) As shown in FIG. 18, it is also possible to adopt a configuration where electronic components, such as electronic circuits of the ICs 20 and 21, the electric connector 22 furnished with the electric terminal pins 23 for inputting/outputting electric signals from/to the outside, etc., as well as the optical module 19 according to the present invention are mounted on the same mount board 6.
(14) As shown in FIG. 19, it is also possible to constitute terminal equipment 32 with the optical module 19 according to the embodiment of the present invention as communicating means of a network etc.
(15) As shown in FIG. 20, FIG. 21, and FIG. 22, it is also possible to adopt a configuration where fixing stud parts are provided outside of an area defined by the lead-shaped electric terminals 15 or the land-shaped electric terminals 16 compliant with the surface mounting process or reflow mounting process.